FIG. 1 shows a conventional screw for using with a printed circuit board (PCB). The screw 5 includes a head 51, a threaded shank 52, and a ferrule 53 having a free end with an axially extended toothed flange 531. The ferrule 53 normally encloses the threaded shank 52 and is retractable into the head 51 under pressure to expose the threaded shank 52, as shown in FIG. 2. To assemble the screw 5 to a PCB 7, first align the ferrule 53 with a through hole 71 provided on the PCB 7, as shown in FIG. 3. Then, apply a downward force on the screw head 51, so that the toothed flange 531 of the ferrule 53 is pressed into the through hole 71, as shown in FIG. 4. And, keep applying the downward force until the toothed flange 531 is completely fitted in the through hole 71 to connect the screw 5 to the PCB 7, as shown in FIG. 5.
While the screw 5 is assembled to the through hole 71 on the PCB 7 in the above-described manner, the following disadvantages exist:
(a) When assembling the screw 5 to the PCB 7, the ferrule 53 is directly aligned with the through hole 71. However, since the head 51 and the ferrule 53 could not be held together through compression during assembling, the ferrule 53 and the head 51 tend to move relative to each other due to the small clearance existed between them. As a result, the ferrule 53 is frequently misaligned with the through hole 71.
(b) Since the screw 5 is very small in volume and the through hole 71 has a relatively small diameter, the alignment of the flange 531 on the ferrule 53 of the screw 5 with the through hole 71 is easily subject to error, preventing the flange 531 on the ferrule 53 from being successfully aligned with the through hole 71 and resulting in a poorly packaged or even a damaged PCB 7.
(c) In the event the flange 531 of the ferrule 53 is not pressed into the through hole 71 in one single operation, the flange 531 tends to be incompletely fitted in the through holes 71 and become deviated or skewed due to inaccurate planeness of the PCB 7.
(d) To assemble the screw 5 to the PCB 7 by pressing the toothed flanges 531 of the ferrules 53 into the through holes 71, the screw 5 is individually fetched to the PCB 7. Therefore, the assembly of a large amount of screws 5 to the PCB 7 could not be efficiently carried out using the surface mount technology (SMT) that has been widely employed in the electronic industrial field.